You should avoid scuba diving whenever a condition could make you lose consciousness, impair breathing or judgment, prevent safe equalization, or increase the risk of serious injury under pressure.
Common reasons to not dive include:
Cold, flu, sinus congestion, blocked nose or ear problems — you may not be able to equalize safely.
Fever, significant infection, vomiting or diarrhea — dehydration and reduced fitness increase risk.
Shortness of breath, chest pain, uncontrolled asthma, or a significant respiratory infection.
Uncontrolled high blood pressure or significant heart/circulation problems until medically cleared.
Recent surgery, hospitalization, or serious illness until a doctor familiar with diving clears you.
Pregnancy — recreational scuba diving is generally not recommended.
Alcohol or recreational drugs — don't dive while impaired or hungover.
Medication that causes sleepiness, dizziness, impaired judgment, or other significant side effects until its compatibility with diving has been assessed.
Extreme fatigue, dehydration, or feeling generally unwell.
Ear pain, difficulty equalizing, vertigo or hearing problems.
After a suspected decompression illness or lung over-expansion injury — stop diving and obtain medical assessment.
After flying: flying before diving generally isn't the concern; flying after diving requires an appropriate surface interval.
A useful rule for instructors and divers is: being physically capable of getting into the water isn't the same as being medically fit to dive. When there's uncertainty about a cardiovascular, neurological, pulmonary, or medication-related issue, a diving-medicine physician should make the call.
